As long as the contacts listed in your iPhone include their full address, the Pocket Doorbell app will use your location data to automatically call or text them when you get to their place.

When you get close to their home the person's name will appear underneath the actual doorbell button on a faux engraved plaque, and if for whatever reason the app's mistaken, you can easily go in and specify who's home you're actually at. I can't remember the last time I've used a doorbell instead of just calling someone as I got near their place, and for just $1, the app saves you a bit of time hunting through your address book. [iTunes App Store via swissmiss]